Motor vehicles are powered by a drive unit, such as an internal combustion engine or an engine-electric motor combination. The drive unit provides a torque output. In vehicles equipped with automatic transmissions, a fluid coupling, such as a torque converter or similar apparatus, transfers the torque from the drive unit to the transmission.
The transmission enables the vehicle to assume a number of different operating modes, ranges, or ratios. In many cases, the transmission provides a number of different forward speed ratios, in addition to neutral and at least one reverse speed ratio.
The transmission includes at least one gear assembly and a plurality of torque transmitting mechanisms such as friction devices, which may include one or more clutches and/or brakes. Typically, an electro-hydraulic control system controls the application or engagement and release or disengagement of the torque transmitting mechanisms, to cause shifts from one range, ratio or mode to another range, ratio or mode in the transmission.
Countershaft transmissions are a type of transmission used in motor vehicles, particularly in commercial vehicles. A variety of countershaft transmissions currently exist. Many currently known countershaft transmissions include a main shaft, and at least one headset gear, which receives torque input from the torque converter turbine or similar apparatus and transfers it to a countershaft. Some existing countershaft transmissions also include a direct shaft, in addition to the main shaft, which bypasses the countershafts and supplies input directly to an output planetary gearset.